WO1998041189A9 - Fabrication of tissue products using a mold formed by solid free-form methods - Google Patents

Fabrication of tissue products using a mold formed by solid free-form methods

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Publication number
WO1998041189A9
WO1998041189A9 PCT/US1998/005724 US9805724W WO9841189A9 WO 1998041189 A9 WO1998041189 A9 WO 1998041189A9 US 9805724 W US9805724 W US 9805724W WO 9841189 A9 WO9841189 A9 WO 9841189A9
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WO
WIPO (PCT)
Prior art keywords
mold
tissue
substitute
powder
molded
Prior art date
Application number
PCT/US1998/005724
Other languages
French (fr)
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WO1998041189A1 (en
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Publication date
Application filed filed Critical
Priority to AU68685/98A priority Critical patent/AU6868598A/en
Publication of WO1998041189A1 publication Critical patent/WO1998041189A1/en
Publication of WO1998041189A9 publication Critical patent/WO1998041189A9/en

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  • the present invention is in the area of methods for fabricating molds to be used in manufacturing molded medical pro ⁇ ucts. wherein the molds are fabricated using computer- aided design (CAD ) in combination with solid free-form fabrication ( SFF technology. More particularly, the present invention is in the area of methods for fab ⁇ caung molds for making molded tissue products.
  • CAD computer- aided design
  • SFF solid free-form fabrication
  • Solid free-form fabrication (SFF) techniques are known which can be used to manufacture complex objects from a variety of materials. These objects can be used as articles of manufacture themselves, or they can be used as molds to create molded articles.
  • SFF methods can be adapted for use with a variety of polymeric, inorganic and composite materials to create mold structures with defined compositions, strengths, and densities, using computer aided design (CAD).
  • CAD computer aided design
  • SFF techniques include stereo-lithography (SLA), selective laser sintering (SLS), ballistic particle manufacturing (BPM ) . fusion deposition modeling (FDM). and three dimensional printing (3 DP).
  • SLA stereo-lithography
  • SLS selective laser sintering
  • BPM ballistic particle manufacturing
  • FDM fusion deposition modeling
  • 3 DP three dimensional printing
  • the present invention can be practiced with any of these SFF techniques.
  • a preferred way of practicing the invention is with the use of three dimensional printing for fabricating the molds of the invention.
  • 3DP is used to create molds which can be used for molding products which comprise tissue from human or other animal sources.
  • SFF techniques can be used to form molds which have at lease one porous portion on the interior surface of the molds, where these porous po ⁇ ions are in communication with the exterior of the molds. According to the teachings of the mvention.
  • tissue mate ⁇ als can De molded into a broad va ⁇ ety of shapes by introducing a mixture containing tissue material mto the interior of a mold according to the teachings of the invention with the tissue material mixed with one or more fluid tissue mat ⁇ x components
  • the fluid tissue matnx component or components can be withdrawn from the tissue mate ⁇ al through the porous portion of the moid, to the exte ⁇ or of the mold.
  • a molded tissue product is thereby produced which can be then released from the mold.
  • one or more additn es may be included in the pore space of the mold of the invention before carrying out molding of a tissue product, and the addi e if used can be removed during the molding process by ithdrawing the additive through the porous structure of the mold to the mold exte ⁇ or
  • the macrostructure and Dorositv ot the mold can De manipulated controlling printing parameters, the t pe of polymer and panicle size, as well as the solvent and/or binder. Porosity of the matrix walls, as well as the mat ⁇ x per se. can be manipulated using SFF methods. especially 3 DP.
  • tissue product to be made can be composed p ⁇ ma ⁇ ly of tissue, can be composed p ⁇ ma ⁇ ly of substitute tissue products, or can be composed of a blend or mixture of natural and synthetic mate ⁇ als mtended to replace tissue in a patient.
  • the fab ⁇ cation of this tissue product using such a mold may be done using either gravity or pressure casting or molding techniques.
  • at least one portion of the inte ⁇ or surface of the SFF prepared mold is porous and in porous communication with the exterior of the mold of the mvention.
  • the mold of the invention allows casting or molding of a tissue product to be more easily carried out because a more fluid mixture of tissue containing mate ⁇ al can be introduced into a mold of the invention. Excess fluid or other excess components of the mixture containing the tissue mate ⁇ al can be drawn from the mold selectively through the porous inte ⁇ or surface portion of the mold, concentrating the tissue product within the
  • Means tor removing the excess fluid or other components can include a simple pump, such as a piston or rotary pump
  • a rough analogy to the method of the invention may be made to slip casting in the ceramics industry, where a ceramic material with excess water (slip) is introduced into a mold for pourabi ty and then the excess water is extracted through the walls of the ceramic mold Bv applying SFF processes to the fab ⁇ cation of a mold, the moid itself can incorporate features which allow selected components of a tissue mixture to be molded to be absorbed or extracted through the walls of the mold.
  • tissue mixture to comp ⁇ se a component to facilitate pouring or lniecting of the tissue mixture into the mold, with the ability to reduce or extract a selected component from the tissue mixture once the mixture is in the mold, enabling improved or augmented implantation or operating characteristics ot the final molded tissue product
  • a SFF fab ⁇ cated mold is used to fully or selective!) control the materials composition of the mold itself as well as the micro- and macro-architecture of the mold
  • the mold ma ⁇ be fab ⁇ cated from a ceramic material which is made with a microstructure that will selectively allow the abso ⁇ tion or extraction of fluid from a tissue mixture, such fluid having been mixed with the tissue to facilitate pou ⁇ ng or injection of the mixture into the mold
  • the porositv of the mold can be ⁇ a ⁇ ed depending on the tissue mixture component to be extracted, or channels or pores may be introduced in certain areas of the mold as the mold is being fab ⁇ cated.
  • a main advantage of the present invention is that it allows a tissue containing mixture to be formulated for flowabihty into a mold, along with the ability to absorb or extract selected components from said mixture du ⁇ ng the molding process, optimizing the actual final tissue product ' s characte ⁇ stics
  • This is a significant advance from conventional approaches for molding tissue products, which are cu ⁇ ently molded using non-porous molds
  • the conventional method for molding tissue products requires that the tissue/additive composition ratio remain the same throughout the molding or casting process and in the final molded or cast product. This results m a compromise being made between the ease of molding and the desired properties of the final tissue product And.
  • Fig. 1 is a schematic drawing ol one embodiment of the three dimensional p ⁇ nting process of the invention
  • Solid free-form iab ⁇ cation methods offer several advantages for constructing molds for molding tissue products Molded tissue products tor implantation into patients can be constructed to fit the individual patient.
  • individual cell type or organ structure SFF methods can be used to selec ely control the composition within the build plane as the mold is constructed by varying the composition of p ⁇ nted material
  • Uncom entional microstructures such as those with complicated porous tetworks or unusual composition gradients, can be designed at a CAD terminal and built througn an SFF process such as 3DP Complex resorbable or erodible tissue products can be built using the method of the invention
  • Three dimensional p ⁇ nting (3DP) is desc ⁇ bed by Sachs, et al , "CAD-Casting: Direct Fab ⁇ cation of Ceramic Shells and Cores by Three Dimensional P ⁇ nting Manufactu ⁇ ng Review 5 (2), 117-126 (1992) and U S Patent No 5,204,055. the teachings of which are mcorporated herein by reterence Suitable devices for carrying out three dimensional p ⁇ ntmg include both those with a continuous jet stream p ⁇ nt head and a drop-on-demand (DOD) p ⁇ nt head.
  • a continuous jet head provides for a fluid that is pressure d ⁇ ven through a small o ⁇ fice. Droplets naturally break off at a frequency that is a function of the fluids properties and the o ⁇ fice diameter Either single jet or multiple et print heads can be used in the method of the present invention The use of multiple jet heads is preferred
  • a DOD p ⁇ nt head utilizes individual solenoid valves that run at frequencies up to 1 2 kHz. Fluid is also pressure driven through these ⁇ alves and a small orifice is downstream of the valves to ensure accurate and repeatable droplet size
  • Both raster and vector apparatuses can be used.
  • DOD a raster apparatus provides that the p ⁇ nt head goes back and forth across the bed with the jet turning on and off.
  • A. continuous jet is alwa ⁇ s on. and a ⁇ ector apparatus is used similar to an x-y p ⁇ nter.
  • 3DP is used to create a solid mold by ink-jet p ⁇ nting a binder onto selected areas of sequentially deposited ers ot powder or particulates
  • the terms "powder " and "particulates are used lnterchangeaoly
  • Each layer is created by spreading a thin layer ot powder over the surface ot a powder Ded
  • a movable powder piston is located within a cv hnder. with a powered roller to deliver dispensed powder to a receiving platform located adiacent to the powder feeder mechanism
  • Operation consists of raising the feed piston a predetermined amount for each increment of powder delivery. The roller then sweeps across the surface of the powder feeder cylinder and deposits it as a thin layer across the receiv ing platform immediately adjacent to the powder feeder
  • the powder feeding piston is then lowered as the roller is brought back to the home position, to prevent any back delivery of powder
  • the powoer piston and cv nder arrangement can also consist of multiple piston cylinders located in a common housing, wnich would be used to dispense multiple powders in the following sequence
  • This method of powder feeding can be controlled manually or be fully automated. Cross contamination of different powders is minimized since each powder is contained in its own separate cylinder.
  • One of the advantages to this method is that only one piston raising/lowering mechanism is required for operation, regardless of the number of powder cylinders. By raising the powder for delivery rather than dropping it from above, problems associated with gravity based delivery systems such as "ratholing”. incomplete feed screw filling/emptying and “dusting” with the use of fine powders is eliminated or minimized since only enough energy is introduced to move the powder up an incremental amount.
  • the powder feeder housing, with its multiple cylinders and pistons, can also be designed as a removable assembly, which would minimize changeover times from one powder system to another.
  • the powder bed is supported by a piston which descends upon powder spreading and printing of each layer (or. conversely, the ink jets and spreader are raised after printing of each layer and the bed remains stationary).
  • Instructions for each layer are derived directly form a computer-aided design (CAD) representation of the component.
  • the area to be printed is obtained by computing the area of intersection between the desired plane and the CAD representation of the object.
  • the individual sliced segments or layers are jointed to form the three dimensional structure.
  • the unbound powder supports temporarily unconnected portions of the component as the structure is built but is removed after completion of printing.
  • the 3DP process is shown schematically in Fig. 1, wherein a 3DP apparatus is indicated generally by the number 10.
  • Powder 12 is rolled from a feeder source (not shown) in stage 1 with a powder spreader 14 onto a surface 16 of a build bed 18 which comprisess powder 28.
  • the thickness of the spread layer is varied as a function of the type of dosage from being produced. Generally the thickness of the layer can vary from about 100 um to about 200 ⁇ m.
  • the print head 22 deposits the binder (fluid) 24 onto the powder layer and the build piston 26 is lowered one layer distance. Powder is again roiled onto the build bed 18 and the process is repeated until the mold is completed (stages 2 and 3 of Fig. 1).
  • the droplet size of the fluid is from about 50 ⁇ m to about 500 ⁇ m in diameter.
  • Servo motors (not shown) are used to drive the various actions of the apparatus 10.
  • the form and its contents be heated or cured at a suitably selected temperature to further promote binding of the powder particles. ⁇ n either case, whether or not further curing is required, the loose unbonded powder particles are removed using a suitable technique, such as ultrasonic cleaning, to leave a finished device.
  • water soluble particulates may be used as an alternative to ultrasonic cleaning. Fabrication of structures with designed pore structures is a challenging task even with additive manufacturing processes such as 3DP. Cylindrical structures with radial pores of hundreds of microns in diameter can be fabricated, however, the removal of loose powder from the na ⁇ ow channels requires a cumbersome manual clean up process. On solution is to employ mixtures of water soluble particulates ( sodium chloride) with polymers used to fabricate specimens. The small particles then leach out to reveal an interconnected porous structure. While this technique is useful in fabricating a network of pores, control of pore architecture is lost. An improvement on this technique is to selectively deposit the soluble phase to form internal soluble patterns prior to building any external features.
  • water soluble particulates sodium chloride
  • Water soluble materials such as poly(ethylene glycol can be deposited on a flat surface prior to spreading a new layer of powder. This enables the process to build walls of soluble material. Loose powder can be spread after completion of the patterning. The external or insoluble features of the specimen can then be built by printing with binder solution. Following the requisite iterations of the patterning and printing processes, produces a dosage form that has intricate internal features that can be dissolved easily when immersed in an appropriate solvent. This concept can be used to fabricate molds with controlled internal pore channels.
  • Construction ot a 3 DP component such as a mold can be v lewed as tne knitting together of structural elements that result from p ⁇ nting individual binder droplets into a powder bed These elements are called microstrucrural primitives
  • the dimensions of the p ⁇ mitives determine the length scale ov er which trie microstructure can be changed Thus.
  • v a ⁇ ed has dimensions near that ot mdiv iduai droplet p ⁇ mitiv es
  • Droplet primitives nave dimensions that are very similar to the width of line primitiv es tormed bv consecutive o ⁇ ntmg of droplets along a single line in the pow ⁇ er bed
  • the dimensions of the line p ⁇ mitiv e depend on the powder and the amount ot bm ⁇ er printed per unit line length
  • a line primitive of about 500 um width is produced if an ink ⁇ et depositing 1 1 cc mm oi methylene chlo ⁇ de is made to travel at about 20 cm/sec ov er the surtace ot a poi caprolactone (PCL) powder bed with 45- "7 5 um particle size
  • PCL poi caprolactone
  • SLA Stereo-lithography
  • SLS Selective Laser Sinte ⁇ ng
  • SFF methods are particularly useful for their ability to control composition and microstructure on a small scale for the construction of these medical devices.
  • the SFF methods in addition to 3DP. that can be utilized to some degree as described herein are stereo-lithography (SLA), selective laser sinte ⁇ ng (SLS). ballistic particle manufacturing (BPM), and fusion deposition modeling (FDM).
  • SLA stereo-lithography
  • SLS selective laser sinte ⁇ ng
  • BPM ballistic particle manufacturing
  • FDM fusion deposition modeling
  • Stereolithography is based on the use of a focused ultra-violet (UN) laser which is vector scanned over the top of a bath of a photopolymerizable liquid polymer material.
  • the UV laser causes the bath to polymerize where the laser beam strikes the surface of the bath, resulting in the creation of a first solid plastic layer at and just below the surface.
  • the solid layer is then lowered into the bath and the laser generated polymerization process is repeated for the generation of the next layer, and so on. until a plurality of superimposed layers forming the desired device is obtained.
  • the most recently created layer in each case is always lowered to a position for the creation of the next layer slightly below the surface of the liquid bath.
  • a system for stereolithography is made and sold by 3D Systems. Inc.. of Valencia. Calif, which is readily adaptable for use ith biocomoa ⁇ ble polymeric materials.
  • SLS also uses a focused laser beam, out to sinter areas of a looseiv compacted plastic powder, the povv ⁇ er being applied layer bv layer, in this method, a thin iayer of powder is spread eve y onto a flat surface with a roller mechanism. The powder is then raster-scanned with a high-power laser beam. The powder material that is struck by the laser beam is fused, while the other areas of powder remain dissociated. Successive layers of powder are deposited and raster-scanned, one on top of another, until an entire part is complete. Each la er is sintered deeply enough to Dond it to the preceding layer.
  • suitable s stem adaptable for use in ma ⁇ ng medical devices is a ailable from DTM Corporation of Austin.
  • SLA and SLS are thus similar in that in both techniques, matter is laminated to make three dimensional shapes.
  • Use of these methods to control composition is limited to one dimensional control since one can only vary the composition of each layer. Nonetheless, these methods can be useful for construction of drug delivery and tissue matrix devices where one dimensional compositional control is ail that is desired or where oniy va ⁇ a ⁇ on in porositv is desired. Controlled porosity can ce built using SLA and SLS simply by specifying the laser path over the layer surface to include only those regions which are to remain in the device.
  • BPM Ballistic Particle Manufacturing
  • FDM Fusion Deposition Modeling
  • BPM uses an ink-jet p ⁇ nting apparatus wherein an ink-jet stream of liquid polymer or polymer composite material is used to create three-dimensional objects under computer control, similar to the way an ink-jet p ⁇ nter produces two-dimensional graphic p ⁇ nting.
  • the device is formed by printing successive cross-sections, one layer after another. to a target using a cold welding or rapid solidification technique. which causes bonding between the particles and the successive layers.
  • This approach as applied to metal or metal composites has been proposed by Automated Dv namic Corporation of Troy. N.Y.
  • FDM employs an x-v plotter with a z motion to position an extrudable filament formed of a polymeric material, rendered fluid by heat or the presence of a solvent.
  • a suitable sv stem is available from Stratasys. Incorporated of Minneapolis. MN
  • BPM. FDM and 3DP are related in the sense that ail three approaches deposit matter in small areas. Thus, they oifer the advantage that locai composition can be specified and constructed for any desired three dimensional profile.
  • the composition control is oniy limited by the resolution of the particular apparatus used for construction.
  • FDM buiid s structures by extruding a fine filament of plastically deformable material through a small nozzie. The nozzle is directed over the built surface by approp ⁇ ate x. v and z motion control so as to yield the desired three dimensional structure
  • BPM invol e s motion control of an ink jet print head to deposit matter in the form of small droplets. Approp ⁇ ate control of where the droplets are p ⁇ nted permits the construction of a desired three dimensional shape.
  • 3 DP uses two sources of mate ⁇ al the mate ⁇ al that makes up the porous layer and the material that is p ⁇ nted.
  • Local composition control using FDM and BPM requires the application of multiple printing or extrusion tools.
  • a similar approach can be followed with 3 DP by using multiple print-heads.
  • multiple droplets may be p ⁇ nted into the same location when using 3DP to increase the local composition of the species contained in the p ⁇ nted solution.
  • Porosity controi using BPM and FDM can be accomplished using procedures similar to those which can be practiced usm ⁇ 3 DP. as desc ⁇ bed herein.
  • Composite ⁇ ev ices can be made bv combining inorganic and organic components.
  • Another method is to mix a noiv mer powder with an inorganic powder.
  • Still another method is to spread polymer powder m the bed. and p ⁇ nt a dispersion of inorganic particles (up to 30 vol% in a solvent which will bind the polymer powder together.
  • apatite particles in chloroform onto a PLA powder bed.
  • a polymer binder with an inorganic dispersion for example by adding 30% by volume particles to a 5% by weight solution of PLA in chloroform.
  • the bed could contain no mate ⁇ ai at all: both the inorganic and organic material could be p ⁇ nted through the nozzle.
  • Bioactive agents which can be incorporated.
  • Bioactive agents that can be incorporated into the molds, although those materials which can be processed into particles using spray drying, atomization. grinding, or other standard methodology, or those materials which can be formed into emulsifications. microparticles. liposomes. or other small particles, and which remain stable chemically and retain biological activity in a polymeric matrix, are prefe ⁇ ed.
  • Bioactive agents also include compounds having principally a structural role, for example, hydroxyapatite crystals in a mat ⁇ x for bone regeneration. The particles may have a size of greater than or less than the particle size of the poivmer particles used to make the matrix.
  • Examples generally include proteins and peptides. nucleic acids, polysaccharides. nucleic acids, lipids. and non-protein organic and inorganic compounds, reie ⁇ ed to herein as 'bioactive agents" unless specifically stated otherwise.
  • These mate ⁇ ais have biological effects including, but not limited to. anti-mflammato ⁇ es. antimicrobials, anti-cancer, antivitals. hormones, antioxidants. channel blockers. and vaccines. It is also possible to incorporate materials not exerting a biological effect such as air. radiopaque mate ⁇ als such as ba ⁇ um. or other ima ⁇ in ⁇ a ⁇ ents
  • Porosity in 3D p ⁇ nted devices can be created either at the level of the feature size (between 10 and 20 microns and greater) or at a sub-feature size level. At the level of the feature size, porosity is controlled by where the features are placed, and thus pore size and shape can vary m three dimensions.
  • Porosity at a subfeature size level can be created in a variety of ways.
  • This procedure may allow interpenetranon of PEO into the surface of the PLA and improve surface properties of the final device. Following p ⁇ nting. the PEO can be leached with water.
  • Modifying surface properties in select regions of the mold is also important and can be accomplished by printing a solution containing surface-active agents into the regions or lines in between where the binder is printed.
  • a "surface-active agent” may be an agent which promotes cell adhesion, such as an RGD peptide. or a material which inhibits cell adhesion, such as a surfactant, for example, polyethylene glycol or a Pluronic.TM. (polypropylene oxid-polyethylene oxide block copolymers).
  • the surface-active agent should in general be contained in a solvent immiscible with the solvent used to print the binder.
  • adhesion peptides such as the RGD adhesion peptide into certain channels (e.g., those for blood vessel ingrowth).
  • An adhesion peptide. such as the peptide having a hydrophobic tail marketed by Telios (LaHoya, Calif.) as Pepfite.TM.. can be dissolved in water and printed into the "voids" using a second set of printing nozzles.
  • Adding water, a relatively non-volatile solvent can alter the kinetics of solvent removal from regions printed with binder. For example, adding water can slow solvent removal by occluding the surface area for evaporation, and can help decrease warpage.
  • the peptide will adsorb out of solution onto the polymer surface.
  • the surface can also be modified to prevent cellular adhesion. This may be accomplished, for example, by printing an aqueous solution of a pluronic.TM. (BASF) or poloxamer.TM. in the voids.
  • the hydrophobic block of such copolymers will adsorb to the surface of the channels, with the hydrophilic block extending into the aqueous phase.
  • Surfaces with adsorbed pluronics.TM. resist adsorption of proteins and other biological macromolecules.
  • Other adhesion-preventing materials are described in Lee. J. H.. J. Kopecek. et al., "Protein-resistant surfaces prepared by PEO-containing block copolymer surfactants.” J. Biomed. Mat. Res, 23:351-368 (1989), the teachings of which are hereby incorporated by reference.
  • 3 DP offers at least three advantages over current technologies for fabricating tissue product molds: (1) tailored macroscopic shapes for making tissue products with complex shapes. (2) well-defined microstructure in the mold, which may include controlled pore size distribution and directionally oriented pores and channels, and (3) incorporation of materials into the mold during its fabrication.
  • tissue material includes both soft tissues such as parenchymal tissue (liver, pancreas, intestine, etc.). blood vessels, skin, and connective tissues such as cartilage and bone.
  • tissue material as used herein may have its origin in any type of animal, including but not iimited to mammalian and human animals.
  • the tissue material mixture or tissue substitute material to be molded can aiso contain one or more synthetic polymers, one or more biopolymers. and/or one or more inorganic materials. The use of these latter materials allows the method of the present invention to be flexible in creating tissue and tissue substitute products which are adaptable to a variety of needs in patients.
  • the synthetic polymers which can be selected for use may be selected from the list consisting of poly(e-caproiactones). poly(hydroxy alkanoates), poly(glycolides), poly(lactides). poly(co-giycolide/lactide). polydioxanone. polyamino acids. poly( ⁇ -glutamic acid), poly(vinyl acetates). poly(vinyl alcohols), poly(ethylene-imines). poly(orthoesters), polyphosphoesters. polyphosphazenes. poly(tyrosine-carbonates), polyanhydrides.
  • polyarylates poly(ethylene glycols), poly(trimethylene carbonate), polyiminocarbonates, poly(oxyethylene-polyoxypropylene), poly( ⁇ -hydroxy-carboxylic acid/polyoxyalkylene), polyacetals, and poly(propylene fumarates).
  • the biopolymers which can be selected for use may be selected from the group consisting of natural proteins (gelatin, collagen, fibrin, elastin. fibronectin. laminin), recombinant proteins (prolastin, pronectin. betasilk), glycosaminoglycans (hyaluronic acid, chondroitin suifate. heparin), carbohydrates (cellulose, chitin, chitosan, dextrins, dextrans), carboxymethylcellulose. sodium hyaluronate, and proteoglycans.
  • the inorganic materials which can be used may be selected from the group consisting of calcium phophates. hydroxyapatites. bioactive glasses, demineralized bone particles, and calcium sulfates.
  • the mold of the invention may be fabricated with the mold itself containing within its matrix certain additives.
  • additives include but are not limited to: pharmaceuticals (antibiotics or anti-inflammatories), hormones (somatotropin), growth factors (bone morphogenetic proteins), peptides (RGD fragments), amino acids, vitamins, enzymes (collagenase. peptidase. oxidase). cellular attractants (fibronectin. vitronectin), living cells (chondrocytes. bone ma ⁇ ow cells), natural tissue extract, fragments of natural tissue, and surface active agents (surfactants. PEG).
  • Components of tissue mixtures being molded which components can be absorbed or extracted through the walls of a mold in accordance with the invention include but are not limited to the following liquid substances or mixtures thereof: water, organic solvents (chloroform, ethanol, other aliphatic alcohols, acetone), polyhydroxy compounds (glycerol, polyethylene glycol. glycerol esters), sugars, fatty acid esters, and natural oils (soybean, castor, linseed, peanut).
  • Materials which can be used to fabricate a mold in accordance with the teachings of the invention include but are not limited to the following materials or mixtures thereof: plastics (polycarbonate, polysulfone. polymethylmethacrylate. polyetherimide), ceramics ( alumina, colloidal silica, zirconia. zircon, silicon carbide), and metals (stainless steel. titanium).
  • interconnected pores or channels will extend from the exterior throughout the interior, typically between 0.15 and 0.5 mm in diameter, which are separated by walls approximately 30 to 100 microns thick, which are either solid or porous with an average pore size of approximately 5 to 40 microns.

Abstract

A method and system for molding a tissue or substitute tissue product in a mold having an exterior surface, and an interior surface, wherein at least one portion of the interior surface is porous and whose pores are in communication with the exterior surface, and wherein said mold can be fabricated using solid free-form fabrication techniques, such as by a three-dimensional printing apparatus (10).

Description

Iills
FABRICAΗON OF ΗSSUE PRODUCTS USING A MOLD FORMED BY SOLID FREE-FORM METHODS
Field of the Invention
The present invention is in the area of methods for fabricating molds to be used in manufacturing molded medical proαucts. wherein the molds are fabricated using computer- aided design (CAD) in combination with solid free-form fabrication ( SFF technology. More particularly, the present invention is in the area of methods for fabπcaung molds for making molded tissue products.
Background of the Invention
Solid free-form fabrication ( SFF) techniques are known which can be used to manufacture complex objects from a variety of materials. These objects can be used as articles of manufacture themselves, or they can be used as molds to create molded articles. The SFF methods can be adapted for use with a variety of polymeric, inorganic and composite materials to create mold structures with defined compositions, strengths, and densities, using computer aided design (CAD).
SFF techniques include stereo-lithography (SLA), selective laser sintering (SLS), ballistic particle manufacturing (BPM). fusion deposition modeling (FDM). and three dimensional printing (3 DP). The present invention can be practiced with any of these SFF techniques. A preferred way of practicing the invention is with the use of three dimensional printing for fabricating the molds of the invention. 3DP is used to create molds which can be used for molding products which comprise tissue from human or other animal sources. SFF techniques can be used to form molds which have at lease one porous portion on the interior surface of the molds, where these porous poπions are in communication with the exterior of the molds. According to the teachings of the mvention. tissue mateπals can De molded into a broad vaπety of shapes by introducing a mixture containing tissue material mto the interior of a mold according to the teachings of the invention with the tissue material mixed with one or more fluid tissue matπx components The fluid tissue matnx component or components can be withdrawn from the tissue mateπal through the porous portion of the moid, to the exteπor of the mold. A molded tissue product is thereby produced which can be then released from the mold. Optionally, one or more additn es may be included in the pore space of the mold of the invention before carrying out molding of a tissue product, and the addi e if used can be removed during the molding process by ithdrawing the additive through the porous structure of the mold to the mold exteπor
The macrostructure and Dorositv ot the mold can De manipulated
Figure imgf000004_0001
controlling printing parameters, the t pe of polymer and panicle size, as well as the solvent and/or binder. Porosity of the matrix walls, as well as the matπx per se. can be manipulated using SFF methods. especially 3 DP.
Summary of the Invention
SFF methods can be used to fabricate a mold hicn can then be useα for the subsequent fabπcation of a tissue product to be used in patients The tissue product to be made can be composed pπmaπly of tissue, can be composed pπmaπly of substitute tissue products, or can be composed of a blend or mixture of natural and synthetic mateπals mtended to replace tissue in a patient. The fabπcation of this tissue product using such a mold may be done using either gravity or pressure casting or molding techniques. Accorαing to the teachings of the present invention, at least one portion of the inteπor surface of the SFF prepared mold is porous and in porous communication with the exterior of the mold of the mvention. The mold of the invention allows casting or molding of a tissue product to be more easily carried out because a more fluid mixture of tissue containing mateπal can be introduced into a mold of the invention. Excess fluid or other excess components of the mixture containing the tissue mateπal can be drawn from the mold selectively through the porous inteπor surface portion of the mold, concentrating the tissue product within the
2 SUBSTITUTE SHEET {RULE 26) .nteπor of the moid. Means tor removing the excess fluid or other components can include a simple pump, such as a piston or rotary pump A rough analogy to the method of the invention may be made to slip casting in the ceramics industry, where a ceramic material with excess water (slip) is introduced into a mold for pourabi ty and then the excess water is extracted through the walls of the ceramic mold Bv applying SFF processes to the fabπcation of a mold, the moid itself can incorporate features which allow selected components of a tissue mixture to be molded to be absorbed or extracted through the walls of the mold. This permits a tissue mixture to compπse a component to facilitate pouring or lniecting of the tissue mixture into the mold, with the ability to reduce or extract a selected component from the tissue mixture once the mixture is in the mold, enabling improved or augmented implantation or operating characteristics ot the final molded tissue product
Using the teaching ot the Dresent invention, a SFF fabπcated mold is used to fully or selective!) control the materials composition of the mold itself as well as the micro- and macro-architecture of the mold For example, the mold ma\ be fabπcated from a ceramic material which is made with a microstructure that will selectively allow the absoφtion or extraction of fluid from a tissue mixture, such fluid having been mixed with the tissue to facilitate pouπng or injection of the mixture into the mold The porositv of the mold can be \ aπed depending on the tissue mixture component to be extracted, or channels or pores may be introduced in certain areas of the mold as the mold is being fabπcated. to allow extraction of tissue mixture components
Figure imgf000005_0001
from selected regions ot the tissue being molded A main advantage of the present invention is that it allows a tissue containing mixture to be formulated for flowabihty into a mold, along with the ability to absorb or extract selected components from said mixture duπng the molding process, optimizing the actual final tissue product's characteπstics This is a significant advance from conventional approaches for molding tissue products, which are cuπently molded using non-porous molds The conventional method for molding tissue products requires that the tissue/additive composition ratio remain the same throughout the molding or casting process and in the final molded or cast product. This results m a compromise being made between the ease of molding and the desired properties of the final tissue product And. since SFF techniques such as three dimensional pπnting are used to fabπcate a mold, product geometries that are unavailable using conventional mold approaches or machimng methods can be readily achieved Such aeometπes include undercuts. o\ erhanεs and recurved surfaces Bπef Descπptton ot the Drawings
A full understanding of fabπcation of molds for use according to the present invention may be had by reading the toliowing detailed description, and may be aided by consideration of the drawing, wherein
Fig. 1 is a schematic drawing ol one embodiment of the three dimensional pπnting process of the invention
Detailed Description ot the Preferred Embodiment
Solid free-form iabπcation methods offer several advantages for constructing molds for molding tissue products Molded tissue products tor implantation into patients can be constructed to fit the individual patient. individual cell type or organ structure SFF methods can be used to selec ely control the composition within the build plane as the mold is constructed by varying the composition of pπnted material Uncom entional microstructures. such as those with complicated porous tetworks or unusual composition gradients, can be designed at a CAD terminal and built througn an SFF process such as 3DP Complex resorbable or erodible tissue products can be built using the method of the invention
Three dimensional pπnting (3DP) is descπbed by Sachs, et al , "CAD-Casting: Direct Fabπcation of Ceramic Shells and Cores by Three Dimensional Pπnting Manufactuπng Review 5 (2), 117-126 (1992) and U S Patent No 5,204,055. the teachings of which are mcorporated herein by reterence Suitable devices for carrying out three dimensional pπntmg include both those with a continuous jet stream pπnt head and a drop-on-demand (DOD) pπnt head. A continuous jet head provides for a fluid that is pressure dπven through a small oπfice. Droplets naturally break off at a frequency that is a function of the fluids properties and the oπfice diameter Either single jet or multiple et print heads can be used in the method of the present invention The use of multiple jet heads is preferred
4 SUBSTITUTE SHEET {RULE 26) A DOD pπnt head utilizes individual solenoid valves that run at frequencies up to 1 2 kHz. Fluid is also pressure driven through these \ alves and a small orifice is downstream of the valves to ensure accurate and repeatable droplet size
Both raster and vector apparatuses can be used. When using DOD a raster apparatus provides that the pπnt head goes back and forth across the bed with the jet turning on and off. A. continuous jet is alwa\ s on. and a \ector apparatus is used similar to an x-y pπnter.
3DP is used to create a solid mold by ink-jet pπnting a binder onto selected areas of sequentially deposited
Figure imgf000007_0001
ers ot powder or particulates In the following descπption. the terms "powder" and "particulates are used lnterchangeaoly Each layer is created by spreading a thin layer ot powder over the surface ot a powder Ded In a preferred embodiment, a movable powder piston is located within a cv hnder. with a powered roller to deliver dispensed powder to a receiving platform located adiacent to the powder feeder mechanism Operation consists of raising the feed piston a predetermined amount for each increment of powder delivery. The roller then sweeps across the surface of the powder feeder cylinder and deposits it as a thin layer across the receiv ing platform immediately adjacent to the powder feeder The powder feeding piston is then lowered as the roller is brought back to the home position, to prevent any back delivery of powder
The powoer piston and cv nder arrangement can also consist of multiple piston cylinders located in a common housing, wnich would be used to dispense multiple powders in the following sequence
1. Line up the first desired powder cylinder with the rolling/delivery mechanism.
2. Increment the movable position piston up to deliver an incremental amount of powder.
3. Activate roller to move powder to receiving platform,
4 Lower the powder piston driving mechanism, 5. Laterally slide the powder feeder housing such that the next desired powder cylinder is lined up with the delivery mechanism.
6. Repeat steps 2. 3. 4 and 5.
7. Continue for as many different powders and/or powder layers as required.
This method of powder feeding can be controlled manually or be fully automated. Cross contamination of different powders is minimized since each powder is contained in its own separate cylinder. One of the advantages to this method is that only one piston raising/lowering mechanism is required for operation, regardless of the number of powder cylinders. By raising the powder for delivery rather than dropping it from above, problems associated with gravity based delivery systems such as "ratholing". incomplete feed screw filling/emptying and "dusting" with the use of fine powders is eliminated or minimized since only enough energy is introduced to move the powder up an incremental amount. The powder feeder housing, with its multiple cylinders and pistons, can also be designed as a removable assembly, which would minimize changeover times from one powder system to another.
The powder bed is supported by a piston which descends upon powder spreading and printing of each layer (or. conversely, the ink jets and spreader are raised after printing of each layer and the bed remains stationary). Instructions for each layer are derived directly form a computer-aided design (CAD) representation of the component. The area to be printed is obtained by computing the area of intersection between the desired plane and the CAD representation of the object. The individual sliced segments or layers are jointed to form the three dimensional structure. The unbound powder supports temporarily unconnected portions of the component as the structure is built but is removed after completion of printing.
The 3DP process is shown schematically in Fig. 1, wherein a 3DP apparatus is indicated generally by the number 10. Powder 12 is rolled from a feeder source (not shown) in stage 1 with a powder spreader 14 onto a surface 16 of a build bed 18 which comprisess powder 28. The thickness of the spread layer is varied as a function of the type of dosage from being produced. Generally the thickness of the layer can vary from about 100 um to about 200 μm. The print head 22 then deposits the binder (fluid) 24 onto the powder layer and the build piston 26 is lowered one layer distance. Powder is again roiled onto the build bed 18 and the process is repeated until the mold is completed (stages 2 and 3 of Fig. 1). The droplet size of the fluid is from about 50 μm to about 500 μm in diameter. Servo motors (not shown) are used to drive the various actions of the apparatus 10.
While the layers become hardened or at least partially hardened as each of the layers is laid down, once the desired final part configuration is achieved and the layering process is complete, in some applications it may be desirable that the form and its contents be heated or cured at a suitably selected temperature to further promote binding of the powder particles. ϊn either case, whether or not further curing is required, the loose unbonded powder particles are removed using a suitable technique, such as ultrasonic cleaning, to leave a finished device.
As an alternative to ultrasonic cleaning, water soluble particulates may be used. Fabrication of structures with designed pore structures is a challenging task even with additive manufacturing processes such as 3DP. Cylindrical structures with radial pores of hundreds of microns in diameter can be fabricated, however, the removal of loose powder from the naπow channels requires a cumbersome manual clean up process. On solution is to employ mixtures of water soluble particulates ( sodium chloride) with polymers used to fabricate specimens. The small particles then leach out to reveal an interconnected porous structure. While this technique is useful in fabricating a network of pores, control of pore architecture is lost. An improvement on this technique is to selectively deposit the soluble phase to form internal soluble patterns prior to building any external features. Water soluble materials such as poly(ethylene glycol can be deposited on a flat surface prior to spreading a new layer of powder. This enables the process to build walls of soluble material. Loose powder can be spread after completion of the patterning. The external or insoluble features of the specimen can then be built by printing with binder solution. Following the requisite iterations of the patterning and printing processes, produces a dosage form that has intricate internal features that can be dissolved easily when immersed in an appropriate solvent. This concept can be used to fabricate molds with controlled internal pore channels. Construction ot a 3 DP component such as a mold can be v lewed as tne knitting together of structural elements that result from pπnting individual binder droplets into a powder bed These elements are called microstrucrural primitives The dimensions of the pπmitives determine the length scale ov er which trie microstructure can be changed Thus. the smallest region over w hich the concentration or bioactive agent can be v aπed has dimensions near that ot mdiv iduai droplet pπmitiv es Droplet primitives nave dimensions that are very similar to the width of line primitiv es tormed bv consecutive oπntmg of droplets along a single line in the powαer bed The dimensions of the line pπmitiv e depend on the powder and the amount ot bmαer printed per unit line length A line primitive of about 500 um width is produced if an ink ιet depositing 1 1 cc mm oi methylene chloπde is made to travel at about 20 cm/sec ov er the surtace ot a poi caprolactone (PCL) powder bed with 45- "75 um particle size Higher print head v eiocities and smaller particle size produce finer lines The dimensions ot the pπmitiv e seem to scale v itn that calculated on the assumption that the liquid binder or solvent needs to fill the pores of the region in the powder which forms the pπmitive
A number of approaches have been descπbed for fabπcating tissue products or substitute tissue products for use in patients It would be advantageous to construct molded tissue products or substitute tissue products with preciselv controlled complicated shapes This can be accomplished bv using SFF techniques to make precisely controlled molds SFF uses computer aided design technologv which allows construction of individual molds for one time use which can have the complicated shape necessarv to mold a tissue product of virtuallv anv desired shape
It is therefore an object ot the present invention to provide a method for molding complex shaped tissue products, tor use in patients
It is another object of the present invention to provide methods and compositions for making complex tissue products of bioerodible or non-bioerodible mateπals or composites for either cell transplantation or matπx-guided tissue regeneration
It is a further object of the present invention to provide methods that operate with high precision and reproducibility to produce molded tissue products.
It is a still further object of the present invention to produce molded tissue products which can selectively encourage the growth of one tissue type over another at specific sites by virtue of control of matrix components within the molded tissue products.
Several other SFF methods can be used in making molds for tissue products in accordance with the teachings of the invention. These include stereo-lithography, selective laser sintering, ballistic particle manufacturing, and fusion deposition modeling. These may briefly be described as follows.
Stereo-lithography (SLA) and Selective Laser Sinteπng (SLS)
SFF methods are particularly useful for their ability to control composition and microstructure on a small scale for the construction of these medical devices. The SFF methods, in addition to 3DP. that can be utilized to some degree as described herein are stereo-lithography (SLA), selective laser sinteπng (SLS). ballistic particle manufacturing (BPM), and fusion deposition modeling (FDM).
Stereolithography is based on the use of a focused ultra-violet (UN) laser which is vector scanned over the top of a bath of a photopolymerizable liquid polymer material. The UV laser causes the bath to polymerize where the laser beam strikes the surface of the bath, resulting in the creation of a first solid plastic layer at and just below the surface. The solid layer is then lowered into the bath and the laser generated polymerization process is repeated for the generation of the next layer, and so on. until a plurality of superimposed layers forming the desired device is obtained. The most recently created layer in each case is always lowered to a position for the creation of the next layer slightly below the surface of the liquid bath. A system for stereolithography is made and sold by 3D Systems. Inc.. of Valencia. Calif, which is readily adaptable for use ith biocomoaπble polymeric materials.
SLS also uses a focused laser beam, out to sinter areas of a looseiv compacted plastic powder, the povvαer being applied layer bv layer, in this method, a thin iayer of powder is spread eve y onto a flat surface with a roller mechanism. The powder is then raster-scanned with a high-power laser beam. The powder material that is struck by the laser beam is fused, while the other areas of powder remain dissociated. Successive layers of powder are deposited and raster-scanned, one on top of another, until an entire part is complete. Each la er is sintered deeply enough to Dond it to the preceding layer. Λ suitable s stem adaptable for use in maκιng medical devices is a ailable from DTM Corporation of Austin.
Figure imgf000012_0001
SLA and SLS are thus similar in that in both techniques, matter is laminated to make three dimensional shapes. Use of these methods to control composition is limited to one dimensional control since one can only vary the composition of each layer. Nonetheless, these methods can be useful for construction of drug delivery and tissue matrix devices where one dimensional compositional control is ail that is desired or where oniy vaπaπon in porositv is desired. Controlled porosity can ce built using SLA and SLS simply by specifying the laser path over the layer surface to include only those regions which are to remain in the device.
Ballistic Particle Manufacturing (BPM) and Fusion Deposition Modeling (FDM)
BPM uses an ink-jet pπnting apparatus wherein an ink-jet stream of liquid polymer or polymer composite material is used to create three-dimensional objects under computer control, similar to the way an ink-jet pπnter produces two-dimensional graphic pπnting. The device is formed by printing successive cross-sections, one layer after another. to a target using a cold welding or rapid solidification technique. which causes bonding between the particles and the successive layers. This approach as applied to metal or metal composites has been proposed by Automated Dv namic Corporation of Troy. N.Y.
FDM employs an x-v plotter with a z motion to position an extrudable filament formed of a polymeric material, rendered fluid by heat or the presence of a solvent. A suitable sv stem is available from Stratasys. Incorporated of Minneapolis. MN
BPM. FDM and 3DP are related in the sense that ail three approaches deposit matter in small areas. Thus, they oifer the advantage that locai composition can be specified and constructed for any desired three dimensional profile. The composition control is oniy limited by the resolution of the particular apparatus used for construction. FDM buiids structures by extruding a fine filament of plastically deformable material through a small nozzie. The nozzle is directed over the built surface by appropπate x. v and z motion control so as to yield the desired three dimensional structure Similarly. BPM invol es motion control of an ink jet print head to deposit matter in the form of small droplets. Appropπate control of where the droplets are pπnted permits the construction of a desired three dimensional shape. 3 DP uses two sources of mateπal the mateπal that makes up the porous layer and the material that is pπnted.
Local composition control using FDM and BPM requires the application of multiple printing or extrusion tools. A similar approach can be followed with 3 DP by using multiple print-heads. Alternatively, multiple droplets may be pπnted into the same location when using 3DP to increase the local composition of the species contained in the pπnted solution. Porosity controi using BPM and FDM can be accomplished using procedures similar to those which can be practiced usmε 3 DP. as descπbed herein.
Formation of Composite Devices
Composite αev ices can be made bv combining inorganic and organic components. In particular, it mav be desired to increase the amount of polymer in the dev ice above that w hich can be obtained by one-pass pπnting of a polymer solution into an inorganic powder bed. for example, by adding a pol mer latex to the printing solution. Another method is to mix a noiv mer powder with an inorganic powder. Still another method is to spread
Figure imgf000014_0001
polymer powder m the bed. and pπnt a dispersion of inorganic particles (up to 30 vol% in a solvent which will bind the polymer powder together. An example of this is to pπnt a solution of apatite particles in chloroform onto a PLA powder bed. Alternatively one can include a polymer binder with an inorganic dispersion, for example by adding 30% by volume particles to a 5% by weight solution of PLA in chloroform. In the extreme, the bed could contain no mateπai at all: both the inorganic and organic material could be pπnted through the nozzle.
Bioactive agents which can be incorporated.
There are essentially no limitations on the bioactive agents that can be incorporated into the molds, although those materials which can be processed into particles using spray drying, atomization. grinding, or other standard methodology, or those materials which can be formed into emulsifications. microparticles. liposomes. or other small particles, and which remain stable chemically and retain biological activity in a polymeric matrix, are prefeπed. Bioactive agents also include compounds having principally a structural role, for example, hydroxyapatite crystals in a matπx for bone regeneration. The particles may have a size of greater than or less than the particle size of the poivmer particles used to make the matrix.
Examples generally include proteins and peptides. nucleic acids, polysaccharides. nucleic acids, lipids. and non-protein organic and inorganic compounds, reieπed to herein as 'bioactive agents" unless specifically stated otherwise. These mateπais have biological effects including, but not limited to. anti-mflammatoπes. antimicrobials, anti-cancer, antivitals. hormones, antioxidants. channel blockers. and vaccines. It is also possible to incorporate materials not exerting a biological effect such as air. radiopaque mateπals such as baπum. or other imaεinε aεents
Controlling Porosity in Molds
Porosity in 3D pπnted devices can be created either at the level of the feature size (between 10 and 20 microns and greater) or at a sub-feature size level. At the level of the feature size, porosity is controlled by where the features are placed, and thus pore size and shape can vary m three dimensions.
Porosity at a subfeature size level can be created in a variety of ways.
(1) Printing a polymer solution onto a bed of particles which are not soluble in the polymer and which can be subsequently leached with a non-solvent for the polymer. In this case, the polymer which forms the device is printed onto a bed of particles such as salt, sugar, or polyethylene oxide. After the printing process is complete, the device is removed from the powder bed and placed in a nonsolvent for the polymer which will dissolve the particles. For example, polvlactic acid in chloroform could be pπnted onto a bed of sugar particles, and the sugar can subsequently be leached with water. (2) Printing a polymer solution onto a bed of panicles which are partially soluble in the pπnted solvent. An example is pπnting a polvlactic acid solution onto a bed of polyethylene oxide particles.
This procedure may allow interpenetranon of PEO into the surface of the PLA and improve surface properties of the final device. Following pπnting. the PEO can be leached with water.
(3) Printing a poiymer solution onto a heated bed of polymer. An example is pπnting polvlactic acid in chloroform onto a bed of PLA particles heated to lOO.degree. C The boiling point of chloroform is 60. degree. C. and it will thus boil on hitting the particle bed. causing a foam to form.
(4) Printing a polymer solution onto a bed contatmng a foaming agent
(5) Printing with solvents which have only a small solubility for the powder. In this manner only a small amount of polymer is deposited at the necks between the particles leaving much of the oπginal porosity in the powder bed. For example. PCL is only slightly soluble in acetone and acetone has a relatively high vapor pressure. Very little poiymer is. therefore, dissolved before the solvent dπes. Thus, the necks formed between the particles are small and the porosity of the resulting component is much like that of the oπginal powder bed.
Molds Having Modified Surface Properties
Modifying surface properties in select regions of the mold is also important and can be accomplished by printing a solution containing surface-active agents into the regions or lines in between where the binder is printed. As used herein, a "surface-active agent" may be an agent which promotes cell adhesion, such as an RGD peptide. or a material which inhibits cell adhesion, such as a surfactant, for example, polyethylene glycol or a Pluronic.TM. (polypropylene oxid-polyethylene oxide block copolymers). The surface-active agent should in general be contained in a solvent immiscible with the solvent used to print the binder.
For example, it may be desirable to incorporate adhesion peptides such as the RGD adhesion peptide into certain channels (e.g., those for blood vessel ingrowth). An adhesion peptide. such as the peptide having a hydrophobic tail marketed by Telios (LaHoya, Calif.) as Pepfite.TM.. can be dissolved in water and printed into the "voids" using a second set of printing nozzles. Adding water, a relatively non-volatile solvent, can alter the kinetics of solvent removal from regions printed with binder. For example, adding water can slow solvent removal by occluding the surface area for evaporation, and can help decrease warpage. On contact with the polymer surface, the peptide will adsorb out of solution onto the polymer surface.
The surface can also be modified to prevent cellular adhesion. This may be accomplished, for example, by printing an aqueous solution of a pluronic.TM. (BASF) or poloxamer.TM. in the voids. The hydrophobic block of such copolymers will adsorb to the surface of the channels, with the hydrophilic block extending into the aqueous phase. Surfaces with adsorbed pluronics.TM. resist adsorption of proteins and other biological macromolecules. Other adhesion-preventing materials are described in Lee. J. H.. J. Kopecek. et al., "Protein-resistant surfaces prepared by PEO-containing block copolymer surfactants." J. Biomed. Mat. Res, 23:351-368 (1989), the teachings of which are hereby incorporated by reference.
Printing the mold with surface active agents while the "walls" of the mold are still "wet" with organic solvent (such as chloroform) can enhance the adsorption of the adhesion-preventing material to the walls and can even allow the hydrophobic block to become blended into the surface, enhancing the stability of the resulting surface modification. For the applications described above. 3 DP offers at least three advantages over current technologies for fabricating tissue product molds: (1) tailored macroscopic shapes for making tissue products with complex shapes. (2) well-defined microstructure in the mold, which may include controlled pore size distribution and directionally oriented pores and channels, and (3) incorporation of materials into the mold during its fabrication.
As used herein, "tissue material" includes both soft tissues such as parenchymal tissue (liver, pancreas, intestine, etc.). blood vessels, skin, and connective tissues such as cartilage and bone. The "tissue material" as used herein may have its origin in any type of animal, including but not iimited to mammalian and human animals.
The tissue material mixture or tissue substitute material to be molded can aiso contain one or more synthetic polymers, one or more biopolymers. and/or one or more inorganic materials. The use of these latter materials allows the method of the present invention to be flexible in creating tissue and tissue substitute products which are adaptable to a variety of needs in patients.
The synthetic polymers which can be selected for use may be selected from the list consisting of poly(e-caproiactones). poly(hydroxy alkanoates), poly(glycolides), poly(lactides). poly(co-giycolide/lactide). polydioxanone. polyamino acids. poly(γ-glutamic acid), poly(vinyl acetates). poly(vinyl alcohols), poly(ethylene-imines). poly(orthoesters), polyphosphoesters. polyphosphazenes. poly(tyrosine-carbonates), polyanhydrides. polyarylates, poly(ethylene glycols), poly(trimethylene carbonate), polyiminocarbonates, poly(oxyethylene-polyoxypropylene), poly(α-hydroxy-carboxylic acid/polyoxyalkylene), polyacetals, and poly(propylene fumarates).
The biopolymers which can be selected for use may be selected from the group consisting of natural proteins (gelatin, collagen, fibrin, elastin. fibronectin. laminin), recombinant proteins (prolastin, pronectin. betasilk), glycosaminoglycans (hyaluronic acid, chondroitin suifate. heparin), carbohydrates (cellulose, chitin, chitosan, dextrins, dextrans), carboxymethylcellulose. sodium hyaluronate, and proteoglycans. The inorganic materials which can be used may be selected from the group consisting of calcium phophates. hydroxyapatites. bioactive glasses, demineralized bone particles, and calcium sulfates.
Optionally, the mold of the invention may be fabricated with the mold itself containing within its matrix certain additives. These additives include but are not limited to: pharmaceuticals (antibiotics or anti-inflammatories), hormones (somatotropin), growth factors (bone morphogenetic proteins), peptides (RGD fragments), amino acids, vitamins, enzymes (collagenase. peptidase. oxidase). cellular attractants (fibronectin. vitronectin), living cells (chondrocytes. bone maπow cells), natural tissue extract, fragments of natural tissue, and surface active agents (surfactants. PEG).
Components of tissue mixtures being molded which components can be absorbed or extracted through the walls of a mold in accordance with the invention include but are not limited to the following liquid substances or mixtures thereof: water, organic solvents (chloroform, ethanol, other aliphatic alcohols, acetone), polyhydroxy compounds (glycerol, polyethylene glycol. glycerol esters), sugars, fatty acid esters, and natural oils (soybean, castor, linseed, peanut).
Materials which can be used to fabricate a mold in accordance with the teachings of the invention include but are not limited to the following materials or mixtures thereof: plastics (polycarbonate, polysulfone. polymethylmethacrylate. polyetherimide), ceramics ( alumina, colloidal silica, zirconia. zircon, silicon carbide), and metals (stainless steel. titanium).
Although mold construction varies with each tissue material type, the methods used for construction will typically be the same, optimized to create appropriate shapes and pore sizes. In general, interconnected pores or channels will extend from the exterior throughout the interior, typically between 0.15 and 0.5 mm in diameter, which are separated by walls approximately 30 to 100 microns thick, which are either solid or porous with an average pore size of approximately 5 to 40 microns.
Modifications and variations of the method and compositions described
17 SUBSTITUTE SHEET {RULE 26) herein will be obvious to those skilled in the art from the foregoing detailed description. Such modifications and variations are intended to come within the scope of the appended claims.

Claims

CLAIMSWhat is claimed is:
1. A method for manufacturing a molded tissue or substitute tissue product, comprising: a) fabricating a mold having an interior surface and an exterior surface, using solid free-form fabrication, wherein said mold has at least one portion of said interior surface which is porous and whose pores are in continuous communication with the exterior surface:
b) filling said mold with a mixture comprising a selected tissue material or tissue substitute, and further comprising an additive at least a portion of which can pass through said pores;
c) drawing a portion of said additive from said selected tissue material through the pores of said mold to form a solid molded tissue or substitute tissue product: and
d) removing said solid molded tissue or substitute tissue product from said mold.
2. The method for manufacturing a molded tissue or substitute tissue product of claim 1, wherein fabricating said mold is carried out using a solid free-form fabrication technique.
3. The method for manufacturing a molded tissue or substitute tissue product of claim 2, wherein fabricating said mold is carried out using three dimensional printing.
4. The method for manufacturing a molded tissue or substitute tissue product of claim 3, wherein the mold comprises a material selected from the group consisting of plastics , ceramics, and metals.
5. The method for manufacturing a molded tissue or substitute tissue product of claim 4, wherein the mixture comprising a selected tissue material or tissue substitute contains a substance selected from the group consisting of synthetic polymers, biopolymers and inorganic materials.
6. A system for manufacturing a molded tissue or substitute tissue product. ΛJmp ϊSflTg:
a) a mold having an interior surface and an exterior surface, wherein said mold has at least one portion of said interior surface which is porous and whose pores are in continuous communication with said exterior surface;
b) a fluid injector for introducing a mixture comprising a selected tissue material or tissue substitute into said mold, wherein said mixture further comprises an additive at least a portion of which can pass through said pores: and
c) a pump for removing a portion of said additive from said mixture by withdrawal through the at least one portion of said interior surface which is porous.
7. The system for manufacturing a molded tissue or substitute tissue product of claim 6, wherein said mold is fabricated using a solid free-form fabrication technique.
8. The system for manufacturing a molded tissue or substitute tissue product of claim 7, wherein said mold is fabricated using three dimensional printing.
9. A mold having an interior surface and an exterior surface, wherein said mold has at least one portion of said interior surface which is porous and whose pores are in continuous communication with said exterior surface.
10. The mold of claim 9, wherein said mold is fabricated using a solid free-form fabrication technique.
11. The mold of claim 10, wherein said mold is fabricated using three dimensional printing.
12. The mold of claim 11, wherein said mold is adapted for coupling to a pump for removing a liquid substance from the interior surface of said mold to the exterior surface of said mold.
PCT/US1998/005724 1997-03-20 1998-03-20 Fabrication of tissue products using a mold formed by solid free-form methods WO1998041189A1 (en)

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